Non-thermal radio emission from O-type stars*
III. Is Cygnus OB2 No. 9 a wind-colliding binary?
School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT, UK e-mail: email@example.com
2 Royal Observatory of Belgium, Ringlaan 3, 1180 Brussel, Belgium
3 National Research Council of Canada, Herzberg Institute for Astrophysics, Dominion Radio Astrophysical Observatory, PO Box 248, Penticton, British Columbia V2A 6J9, Canada
4 Erasmus University College, Nijverheidskaai 170, 1070 Brussel, Belgium
Accepted: 6 March 2008
The star Cyg OB2 No. 9 is a well-known non-thermal radio emitter. Recent theoretical work suggests that all such O-stars should be in a binary or a multiple system. However, there is no spectroscopic evidence of a binary component. Re-analysis of radio observations from the VLA of this system over 25 years has revealed that the non-thermal emission varies with a period of 2.35±0.02 yr. This is interpreted as a strong suggestion of a binary system, with the non-thermal emission arising in a wind-collision region. We derived some preliminary orbital parameters for this putative binary and revised the mass-loss rate of the primary star downward from previous estimates.
Key words: stars: individual: Cyg OB2 No. 9 / stars: early-type / stars: mass-loss / radiation mechanisms: non-thermal
© ESO, 2008